1. Field of the Invention
The present invention relates to a prismatic battery and a method for manufacturing the same.
2. Description of Related Art
In recent years, accompanying the development of portable electronic equipment, the roles of batteries including primary batteries and secondary batteries have become increasingly important. Competition to make equipment on which a battery is mounted have a smaller size and a higher function has become fierce. Mainly, batteries capable of achieving a small size, high volume and high output have been demanded in the market.
As such batteries, conventionally, rectangular batteries or cylindrical batteries have been common. Each shape has respective features, for example, high space efficiency for stacking and integrating, etc. in integrating a plurality of batteries, high productivity, and the like. However, in other words, each shape has respective problems. In rectangular batteries, for example, sealing the battery is more difficult as compared with the case of cylindrical batteries. Furthermore, in cylindrical batteries, for example, in stacking and integrating a plurality of batteries, a larger dead space is formed as compared with the case of rectangular batteries.
In order to solve these problems described above, a battery including a battery case having a prismatic body for accommodating an electrode plate group, etc. and a cylindrical head portion for sealing the battery is disclosed (see, for example, JP63-207048A, JP2002-141100A, and JP2002-208380A, etc.). By allowing a battery to have such a configuration, a battery having high property having both advantages of a rectangular battery and a cylindrical battery is expected to be provided.
Furthermore, JP7-226212A discloses a technique for accommodating an electrode plate group, which was formed so as to have a rectangular parallelepiped shape, into a prismatic battery case. More specifically, as shown in FIG. 18A, a cylindrically wound electrode plate group 102 is heated and pressed from all directions by using molds 103 disposed at intervals of 90° to allow the electrode plate group 102 to have a rectangular parallelepiped shaped cross section.
An example of a method for actually forming a battery disclosed in JP63-207048A and JP2002-208380A includes a method of forming a battery case by forming an opening end portion of a prismatic can into a cylindrical shape. However, at that time, a can may be swollen or wrinkled. For example, FIG. 17 is a schematic view showing an example of a conventional battery case having a prismatic body portion for accommodating an electrode plate group and an electrolyte, and a cylindrical head portion. When an opening end part of a prismatic can is just molded in a cylindrical shape, the can may be swollen in a region A or wrinkled in a region B in a battery case 101 shown in FIG. 17. If such defects occur, it becomes difficult to seal the battery, or liquid leakage may occur due to a crack in a battery case generated in the part where defects occur. Furthermore, from the viewpoint of productivity such as yield, etc. the reduction in such defects is demanded.
In order to solve these problems, for example, in the method disclosed in JP2002-141100A, an electrode plate group is accommodated in a cylindrical shaped battery case, its opening end is closed and sealed, and then a prismatic body portion is formed. However, in this method, when the prismatic body portion is formed, the deformation of the electrode plate cannot be avoided and short-circuit or dropping-off of active materials may occur.
Furthermore, in the method shown in JP7-226212A, in a case where a winding end portion 104 of the electrode plate group 102 is located on a side of the rectangular parallelopiped shape after molding, when the cylindrical plate group 102 is molded into a rectangular prallelopiped shape (FIG. 18A) or the electrode plate group 102 is inserted into the prismatic battery case 105, an internal short-circuit or defective insertion into the battery case 105 may occur.